Housing
What size is your tank? 10 gallens
What temperature is your tank? 78 Degrees F
Does your tank have a filter? Yes
Does your tank have an air stone or other type of aeration? No
Is your tank heated? Yes
What tank mates does your betta fish live with? Have a sorority tank with four additional female betta

Food
What type of food do you feed your betta fish? Pellets, bloodworms (as a treat)

How often do you feed your betta fish? Pellets twice a day (AM, PM), special blood worm treat once on Sundays in place of meal, let fish fast on Mondays to prevent constipation since that has been an issue with one girl

Maintenance
How often do you perform a water change? Started tank Christmas week and have done one full water change and one 25% change this week since this is a new tank
What percentage of the water do you change when you perform a water change? Plan to do 25% 1x a wk from here on out
What type of additives do you add to the water when you perform a water change? Initially added bacteria starter and stress coat; also added bacteria starter with first full water change; now just add stress coat/water conditioner

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Symptoms and TreatmentHow has your betta fish's appearance changed?
Wednesday--Blue became less active this past Wednesday and began hiding under the bridge we have full-time except to come up for air. On Thursday she was no longer eating and not acting like her active self (I would consider her a co-alpha).

Friday--Friday morning she was opening and closing her mouth repeatedly like she was struggling to breathe, so I removed her from the tank (had to coax her from under the bridge) and put her in a small clear plastic cup to be able to observe her. I also noticed that she looked "beat up" and had bad fin damage. She does not bite herself and it wasn't fin rot, so she must have been attacked. I added a few drops of stress coat and kept the watcher shallow so that it would be easier for her to get to the top and breathe. At this point, she looked like she was continually struggling to breathe and was not eating.

Sat--I did a water change on Sat. (took water from her tank) since it was a small cup and I wanted to keep her warm. I gave her a bit of blood worm hoping to coax her to eat, but she wasn't interested. Hubby and I decided we would put her down (Hubby read about clove oil on this forum) on Monday if she didn't show improvement or go out and buy a mini heater for our 1/2 gallon tank and set up a betta hospital for her.

Sunday--Hubby told me she died around 9:00 this morning. She started swimming frantically like she was going to jump out of the tank for a few minutes and then just stopped moving and died. I hated to hear she died so violently, but I wanted to give her every chance to "turn around" before having to decide to put her down.

Hubby and I suspected dropsy, but she didn't have the pine cone appearance we saw in pictures here on the forum until this morning. She also appeared bloating despite not having ate for several days. Additonally, she spent part of yesterday and this morning with her nose pointed to the surface, almost straight up. Our other bettas are happy and healthy except that our one crown tail (young) gets constipated easily after eating one pellet. We did have a betta suddenly die for unknown reasons a week ago and all of her fins had been eaten off when we discovered her. We worry that Blue may have been the culprit and got sick as a result.

How has your betta fish's behavior changed? Lying at bottom of tank under bridge, opening and closing mouth rapidely, not eating
When did you start noticing the symptoms? Wednesday
Have you started treating your fish? If so, how? Removed Blue from tank Friday morning; kept her isolated in cup; no meds given other than drops of Stress Coat
Does your fish have any history of being ill? I bought her Christmas Eve from a local reputable pet store and she seemed healthy though she was kept in one of those horrible small cups. She had shown no signs of illness until this past week.
How old is your fish (approximately)? She was the largest of the group, so I would guess she was an adult when we bought her though not very old since she was very active and kept up with the younger ones fine.

Here is the big question...

What did Blue die from and what can we do to prevent the rest of our sorority from getting sick?
As new sorority tank owners, are there things Hubby and I should be doing and are not (besides regular water changes, testing for ammonia, etc.)?

Sadly, we often will never know why our fish die-With that said, my best guess would be due to compromised immune response secondary to stress. We have a lot of pathogens in our systems and not all pathogen will become pathogenic-unless the conditions are right-The big one being stress that compromises the immune response.

As posted by registereduser, it sounds like your tank isn't fully cycled since you don't have nitrates-unless you have a lot of active growing plants. Plus you are making complete water changes??? When you say "Full water change" do you mean you remove everything or just most of the water.

Since your tank is filtered, you don't need to make full or complete water changes. In a 10gal filtered tank-without live plants with your stocking level-I would recommend 50% weekly with vacuum in all places you can reach without moving anything once the nitrogen cycle has established. Until then-along with that 50% with vacuum-make a 50% water only based on test results of Ammonia, nitrite 0.25ppm or greater. It can take up to six weeks to establish the nitrogen cycle.

As a general rule-anytime you find a dead fish or sick fish that your move to QT-Make a 50% water only.

With a sorority tank-I have found that by having tall items in the tank that go all the way to the top in several different places can help-This can break the line of sight and allow the less dominate female a way to the top without being seen. While lower level hide outs are good-since this is a surface dwelling species-having lots of cover at the surface is important.

Tank is definitely not cycled. By those readings it is just beginning.. I would expect it to be farther along since you've had it almost a month, but cycling can take up to 2 months. What filter are you using and how are you maintaining it?

You need to do a 50% water change with siphon to clean the gravel today and then keep dong this every time you see either ammonia or nitrite hit as little as .25ppm - test daily. Eventually a once weekly 50% w/ vac will be all that's needed, but for now it's really important to keep on top of changes.

Sororitys can be hard to maintain.. They need lots of coverage and places to hide. They also do better in 20g with 6+. Sometimes despite best efforts, they still don't work out. This may be of help: http://www.bettafish.com/showthread.php?t=29402

She may have died from damage from the attack. Dropsy is actually organ failure. It's often times caused by an internal infection, but not always. Prior to the attack she was also acting like she was suffering from ammonia poisoning. She could also have gotten too stressed.

Since your tank is filtered, you don't need to make full or complete water changes. In a 10gal filtered tank-without live plants with your stocking level-I would recommend 50% weekly with vacuum in all places you can reach without moving anything once the nitrogen cycle has established. Until then-along with that 50% with vacuum-make a 50% water only based on test results of Ammonia, nitrite 0.25ppm or greater. It can take up to six weeks to establish the nitrogen cycle.

Thank you for the kind words and the advice.

We are using the Sentry AQ Mardel test kit we picked up from Petsmart. The info I gave earlier might be a little off. Our Ammonia is still 0 and says Ideal according to our chart. Our NitrAtes are a very light pink and on our scale is goes from a white 0 (safe) to a Pink 20 (caution) so with it being a light pink we are guessing it's in the 5-10 range.

Our nitrItes still read as 0, the next step is 0.5 and is caution.

After Rainbow died we did a 2/3 water change. So thank you for letting us know about doing just a 1/2.

Blue was a good little pet, we thought she was co-alpha with Red. BTW Red has SBD which we learned how to treat here. We watch what Red eats and make sure she is separated while eating. She used to steal food from the other girls.

We think Blue either killed Rainbow or just munched on her after she passed. We didn't know if Rainbow was sick and if Blue did munch on her would that make Blue sick too.

We have no idea who might have attacked Blue. After reading some of the other posts we learned that bettas might chew their own tails or maybe other things to self harm. Up till this she was happy. She explored the entire tank. She chased Rainbow and Pinkie around when they got in her space. So to see her do that one day and the next morning hide under the bridge was a little shocking.

Thank you for all your help and we'll follow the advice given and anymore you folks might have. We'll also keep you updated on things and how they are doing. Thanks!